1. Field of the Invention
The present invention relates to an apparatus and method for transmitting moving image data.
2. Description of the Related Art
In recent years, a great improvement has been achieved in performance associated with communication environments and data processing environments. This has made it possible to realize a streaming technique to provide a real-time distribution of multimedia data such as moving image data or audio data via a network. The realization of the streaming technique allows users to enjoy viewing live TV programs or recorded video/TV programs supplied in a streaming format. Users are also allowed to view on-demand TV/video programs provided by the streaming technique.
In service such as real-time distribution of an audio or video program, a video telephone, etc., in which a transmission delay or a transmission failure is not allowed, a QoS (Quality of Service) control technique is very important to guarantee performance in terms of a communication speed, a delay time, jitter, a packet loss rate, etc.
For example, TCP (Transmission Control Protocol) provides a retransmission control scheme that detects an occurrence of a failure to receive data at a receiving end and retransmits the data to the receiving end.
It is known to use an intra refresh scheme to avoid error propagation. For example, in a technique disclosed in Japanese Patent Laid-Open No. 06-237451, if a packet is lost during transmission of moving image data, a refresh request is sent from a receiving end to a transmitting end. Upon receiving the refresh request, intraframe encoded moving image data is immediately transmitted from the transmitting end. This makes it possible to obtain a normal image at the receiving end even when a loss of a packet occurs.
However, depending on the status of a network, there is a possibility that retransmission of lost moving image data fails to avoid degradation in image quality. Besides, retransmission of lost moving image data results in an increase in transmission.
When moving image data lost somewhere in a transmission path is retransmitted, if the network is in a congested state, there is a possibility that the retransmitted moving image data does not arrive in time for playback (decoding). In this case, moving image data that is not used in playback is retransmitted, and thus a useless increase in transmission occurs.
When a loss of moving image data in a transmission path is detected, performing of intra refresh prevents error propagation. However, the intra refresh does not prevent an occurrence of degradation in image quality at a frame itself corresponding to the lost moving image data.